So the data you have represents the height per week
Time (weeks) Height (cms)
3 4.6
4 5.8
7 9.4
So, In one week, the plant grew 5.8 - 4.6 = 1.2 cms
In the next 3 weeks the plant grew 9.4 - 5.8 = 3.6 cms
So in totality the plant growth was measured for 4 weeks and it grew by 4.8 cms (from 4.6 to 9.4)
So the growth rate per week is the ration of total increase/# of weeks
so we get the growth rate per week = 4.8/4 = 1.2 cms per week
Time (weeks) Height (cms)
3 4.6
4 5.8
7 9.4
So, In one week, the plant grew 5.8 - 4.6 = 1.2 cms
In the next 3 weeks the plant grew 9.4 - 5.8 = 3.6 cms
So in totality the plant growth was measured for 4 weeks and it grew by 4.8 cms (from 4.6 to 9.4)
So the growth rate per week is the ration of total increase/# of weeks
so we get the growth rate per week = 4.8/4 = 1.2 cms per week